1. Field of the Invention
The present invention relates generally to a liquid crystal display device, and more particularly to a transflective liquid crystal display device having a reflective display region and a transmissive display region.
2. Description of the Related Art
A display device using a liquid crystal element is not self-luminous, unlike a CRT (Cathode-Ray Tube) or an EL (Electroluminescence) device. As a liquid crystal display device which enables luminous display, there is known a transmissive liquid crystal display device, wherein a backlight is disposed on the back side of the liquid crystal element and the backlight illuminates the back side of the liquid crystal element. In usual cases, however, the backlight consumes more than 50% of the total power which is consumed by the liquid crystal display device. As a liquid crystal display device which can reduce power consumption, there is known a reflective liquid crystal display device, which effects luminous display by using only ambient light, and this reflective liquid crystal display device has been applied to mobile information devices which are, in usual cases, used outdoors or carried by users. A drawback of the reflective liquid crystal display device is that when ambient light is dark, reflective light for effecting display decreases and the visibility considerably deteriorates. On the other hand, the transmissive liquid crystal display device has such a drawback that the visibility deteriorates when ambient light is very bright, for example, in fine weather.
To solve these problems, there is known a transflective liquid crystal display device wherein a reflective display part and a transmissive display part are separately provided in each of pixels.
In a dark place, the transflective liquid crystal display device functions as a transmissive liquid crystal display device which displays an image by selectively passing backlight through the transmissive display part in each pixel. In a light place, the transflective liquid crystal display device functions as a reflective liquid crystal display device which displays an image by selectively reflecting ambient light by means of the reflective display part in each of the pixels. Thereby, power consumption can greatly be reduced.
Various liquid crystal display methods are applicable to the liquid crystal display device, if a variation in liquid crystal alignment is utilized in such methods. For example, a TN (twisted nematic) mode and a STN (super-twisted nematic) mode, in which polarizers are used, are adopted in reflective liquid crystal display devices. In recent years, a phase-transition guest-host (GH) mode, which can realize bright display since no polarizer plate is used, has been developed.
In a multi-domain VAN (Vertical Alignment Nematic) (MVA) mode, liquid crystal molecules in the vicinity of the surface of an alignment film are vertically aligned by adopting a vertical alignment treatment, and the birefringence index of the liquid crystal layer becomes substantially zero. Thus, black of an adequate level can be displayed and a high contrast can be obtained. In addition, the design for compensating a viewing angle is relatively easy, and a wide viewing angle can be realized. Furthermore, a rubbing alignment treatment process, which has conventionally been considered to be a possible cause of defects, such as electrostatic discharge damage, can be dispensed with. Therefore, the MVA mode has attracted particular attention in these years.
However, if the MVA mode is applied to the transflective liquid crystal display device, the direction of electric field, which is applied to the liquid crystal layer, and the elastic energy due to the interface shape become complex. It is thus difficult to obtain fixed guidelines relating to the alignment state of liquid crystal molecules in association with the arrangement of ridge-like projections and slits. In some cases, the arrangement of liquid crystal molecules may be disturbed in each domain, and it is difficult to stably form a plurality of domains in one pixel.
The present invention has been made in consideration of the above-described problems, and the object of the invention is to provide a liquid crystal display device which can have wide viewing-angle characteristics by virtue of stable domain division, can suppress a decrease in light transmissivity due to, e.g. disturbance of the alignment direction of liquid crystal molecules, and can perform transmissive display and reflective display with high display quality.